texts: Using emission lines to determine redshift of a quasar

texts:
I am attempting this past paper question and am not sure how to tackle this, this is not homework! :)

  The spectrum of a distant quasar shows two broad emission lines with observed
  wavelengths of 317.7nm and 404.7nm. The strongest lines are most likely to be either Lyman-α with a rest wavelength 121.6nm, CIV with a rest wavelength of 154.9nm or MgII with a rest wavelength of 280.0nm.

  (a) What is the redshift of the quasar? Please show your working.

  (b) What two lines have been detected?

  (c) The two lines have widths of 10nm and 20nm respectively. If I have measured
  the mass of the black hole in the quasar to be 10^9Msun, how far from the centre of the quasar are the regions of ionised gas responsible for the emission lines?
  Please specify any assumptions that you make to obtain your result.

I am assuming I must find z to be the ratio of the change in wavelength to the rest wavelength. However I'm unsure of how to identify these in the question.


texts: How Does IceCube Trace a Neutrino to its Source?

texts:
I read the following claim in an article (Lisa Grossman, "Origin of Cosmic Oddities Proposed," Science News, February 17, 2018, 8).

  ... IceCube has already traced an especially high-energy neutrino to a single active black hole ... IceCube [Neutrino Observatory in Antarctica] could eventually trace neutrinos back to [active black holes in] galaxy clusters.

Aren't galaxy clusters at least millions of light-years from Earth?

Such neutrinos took millions of years to get to Earth.
Other sources could have been in the path of the neutrinos in such a distant past.
Are neutrinos affected by gravitational lenses as light can be?
Is such tracing possible because neutrinos react so weakly with matter?


texts: Computing the local orbital frame vector directions in a geocentric reference frame

texts:
In the context of the study of a cubesat (little satellite), I am asked to define the local orbital frame and compute the local orbital frame vector directions as a function of time :

Here the context :

Anyone could give me some tracks or links to find the answer of part 2.1 Local orbital frame ? this would be kind.

Regards


texts: Is Polar Lights observation possible at the latitude of 56° N?

texts:
Back in 2002, me and my friends observed a green glow in the sky at night in the form of giant slow moving spurts of flame, looking more dense near the horizon and more blurred at height. It was surrounding the area, not just on one side, as I see on most of the imagery available. It was bright enough to see for several people sitting around a bonfire.

Is it possible for the natural phenomena, 'Aurora Borealis' take place as far south as 56° N, 37° E; in a Moscow suburb, Russia?


texts: When and where are we exposed to most cosmic radiation?

texts:
I understand the mechanical dynamics of being faced away from the Sun at night, having a lower altitude, not being in the weak points at the poles in the atmosphere, being in a valley and others decreasing cosmic radiation.

Are the particular areas on Earth where cosmic radiation is amplified or unprotected by the magnetosphere because of the  lensing effect on cosmic rays either by location or angle of the sun?


texts:
I was amazed when my teacher told me that in space, time is define as a coordinate. It means we can define something  with a four coordinate system with "negative time" $-t$ as easily as we can say $-x$. Assuming that we can, what will this suggest?

Edit:) yesterday I saw so many answer on it, create one more doubt in me, that how do I define a origin in space, because there nothing to which I compare, suppose I have two events A and B, how can I say A occur before B, if I say this, from which reference I am comparing it....


texts: What would happen if a body were to fall into a neutron star?

texts:
We know neutron stars as a very massive object with extremely strong gravitational forces that composes mostly of neutrons.

I couldn't help but wonder, what would happen if an object fell into a neutron star, what would become of it? Will it turn it into neutrons as well? And will be any sort of accompanying radiation emission?


texts: Reproduce and plot myself from a paper with appropriate scripts and Fisher/Covariance matrixes

texts:
I would like to reproduce and plot myself the figure below. This plot, even it begins to date, is full of informations for me. The paper is located here : paper Suzuki et al. 2011

I have contacted the 3 main authours of the paper (Suzuki et al. 2011) but none gave me an answer.
I know Fisher formalism and Python frameworks like GetDist or other tools to generate this kind of plot but I have not the data (Fisher or Covariance matrixes) allowing to reproduce this plot myself. It is quite frustrating.
If someone could help me to plot them, that is to say, to get the Python scripts and the Fisher/Covariance matrixes used, I would be grateful since I begin to desperate.
ps : others complementary figures would be reproduced also like below :


texts:
I am looking for a catalog of low redshift galaxies (preferably SDSS) with information on line fluxes and stellar mass. My Google searches keep pointing me to work by the Portsmouth group, so I downloaded some of the fits files listed at the bottom of the page, but there are no line fluxes in those files, even though they seem to suggest that the line fluxes are being made available... I was just wondering if what I'm looking for is publicly available and if I'm looking in the right place? Their page links to a table that lists all the key words I would like to use, but I'm not sure how to obtain the data.
In one of the files I downloaded (portsmouth_emlinekin_full-26.fits) there's a column called BPT, which lists the BPT classification (Seyfert, LINER, Star forming...), so I was expecting to also find the "building blocks" ([OIII], [NII], [SII], [OII], Halpha and Hbeta line fluxes) of the BPT diagram. Is it usually necessary to contact the authors for stuff like this?
Would be very grateful to learn about using publicly available survey data from a more experienced scientist :)


texts: How to query a region on the sky when given only ecliptic coordinates?

texts:
I am new at using the Python packages astropy/astroquery and what I want to achieve is to use it to find stars that lay on the TESS continuous view zone (CVZ).

I know the CVZ is centered at the south pole of the ecliptic an I would like to use the function astroquery.mast.Observations.query_region() to query a region centered at the coordinates of the pole. Such function uses coordinates in the international celestial reference system (ICRS) so first I have to convert from the ecliptic frame the pair $(\text{lon}=0^\circ , \text{lat}=-90^\circ)$.

I tried the conversion using the function transform_to(ICRS),however, it returns the following error:

  UnitsError: The input HeliocentricTrueEcliptic coordinates do not have length units. This probably means you created coordinates with lat/lon but no distance.  Heliocentric<->ICRS transforms cannot function in this case because there is an origin shift.

Could someone elaborate a bit more about the "distance" and "origin shift" mentioned in the error message and how to correct it?


texts: How accurate is the "Equation of time" (mean time to actual solar time)? And how much can it vary from the average?

texts:
At Wikipedia, they give equal values (9.87 min) for all four extremes – both troughs and both crests – caused by the obliquity of the ecliptic as seen in the graph below, where the purple dashed line is what is caused by the obliquity of the ecliptic.  But the duration of the four seasons are not equal, as you can see here. So what effect does it have on the equation of time?
Also, the time from a perihelion to the next aphelion is not always the same as the time from that aphelion to the next perihelion, as seen in this almanac. As a consequence, the greatest delay of noon caused by the eccentricity of the orbit shouldn't be equal to its greatest advance. So how big can the difference be?
Also, the dates of the perihelion and aphelion, as well as the actual sun-earth distance at these events aren't the same each year, as seen in the above reference. So the actual latest and earliest noon varies from the given dates. My question is, how much can they vary?


texts:
I have received a new Celestron Powerseeker 127 (a 5' short Newtonian), however it came without a tripod mount.

Ideas or suggestions on how to procure the right mount our a suitable alternative would be most welcome.

I am looking for sourcing tips rather than advice on how to choose a tripod.


texts: apparent and absolute magnitude of meteors and space debris

texts:
I have a question regarding the apparent and absolute magnitude of space debris objects or meteors reentering the earth's atmosphere. I already understand the difference between apparent and absolute magnitude. The absolute magnitude is the brightness of the object if the object is at a distance of 100km and at zenith. And the apparent magnitude is how bright the objects appears to the observer.
But how can I determine the apparent magnitude of an objects observed from an observer? The objects has the distance $d$, the zenith distance $Z$ and the height $h$. On the internet I found the following equation:
$$
M = m +5  \log(\cos(Z))
$$
$M$ = absolute magnitude, and $m$ = apparent magnitude. I posted a picture below.
But how is this equation derived? I do not understand the equation. What can I do, if the height $h$ of the objects does not equal 100 km?
The book where i found this is "The Observer's guide to Astronomy" (Volume 2) pages 659 to 660!
https://books.google.de/books?id=TXc54LfKsSQC&pg=PA659&lpg=PA659&dq=zenithal+magnitude&source=bl&ots=fPeMVD1sOq&sig=ACfU3U26N79Xm-qsiC4ocoMHHcCw9Lc3jw&hl=de&sa=X&ved=2ahUKEwiP2Lf3v-bpAhVk-ioKHQ0oD5wQ6AEwAXoECAsQAQ#v=onepage&q=zenithal%20magnitude&f=false


texts:
The NASA Goddard news item NASA to Demonstrate New Star-Watching Technology with Thousands of Tiny Shutters says:

  The technology, called the Next-Generation Microshutter Array (NGMSA), will fly for the first time on the Far-ultraviolet Off Rowland-circle Telescope for Imaging and Spectroscopy, or FORTIS, mission on October 27. The array includes 8,125 tiny shutters, each about the width of a human hair, that open and close as needed to focus on specific celestial objects.

Question: What is an "Off Rowland-circle Telescope"?


texts: When using adaptive optics, what is the shortest timescale of atmospheric changes in refractive index that astronomers have to deal with?

texts:
I am interested in the astronomer's need for speed in wavefront correction, especially when measuring in NIR and visible domain.

What is the fastest abberation coming from atmospheric turbulence in any measurement setting (sun observation during day, night-time observations)? Does any astronomer need correction in the visible spectrum beyond e.g. 100 Hz?
Are fast systems practically limited by spatial resolution of the sensor?
Is there any way to get a quantitative overview how widespread adaptive optics is in astronomy today and which setups are currently in use?

Thank you for your thoughts!


texts: Tonight high up in the night sky, it was 8.20 precisely, I saw a bright orange light floating slowly across the sky ,occasionally slowing as if looking for something and flickering, it was too high up and far away to see an exact shape, but it looked like a star, so was it a star, do we have bright orange stars


texts: How to map moon phase number + "lunation" to moon phase name?

texts:
I am querying an API (weatherbit) which returns a moon phase number which looks like this:
0.9594168
For the 16 days I look at the numbers vary from 0.006 to 0.99.
I have 8 "moon phase" icons for the full, crescent, gibbous, etc. phases.  Filenames are the phase names.
How can I map the moon phase number to the phase names so I can use images with those names appropriately.
Final Update: Use moon_phase_lunation (instead of moon phase number) only
Here is the final js-react code which seems to be working well so far:
import React from 'react';
const Moon = ( data ) => {
  const lunation = Number(data.moon_phase_lunation);
  let imageToUse;
  if (lunation <= .06) imageToUse = 'new';
  if (lunation > 0.06 && lunation <= .19) imageToUse = 'waxing_crescent';
  if (lunation > 0.19 && lunation <= .31) imageToUse = 'third_quarter';
  if (lunation > 0.31 && lunation <= .44) imageToUse = 'waxing_gibbous';
  if (lunation > 0.44 && lunation <= .56) imageToUse = 'full';
  if (lunation > 0.56 && lunation <= .69) imageToUse = 'waning_gibbous';
  if (lunation > 0.69 && lunation <= .81) imageToUse = 'first_quarter';
  if (lunation > 0.81 && lunation <= .94) imageToUse = 'waning_crescent';
  if (lunation > 0.94 ) imageToUse = 'new';
  const imageURL = `/moonIcons/${imageToUse}.png`;
  return (
    <>
      <img src= { imageURL } width="20px" height="20px" />
    </>
  );
};

export default Moon;


texts: Have there been successful attempts at spotting Neptune with the naked eye?

texts:
As pointed out here, the limit of naked eye visibility for people with extremely good night vision is about magnitude 8.5. Neptune at opposition is much brighter at magnitude 7.7, so it should be visible to people with good eyesight. Astronomer Brian Skiff, made an attempt about a decade ago, he failed to spot it. He said that it should be relatively easy to spot from the Southern Hemisphere as it is high in the sky viewed from there.

But surely many other people with good eyesight who are capable of seeing faint stars of magnitude 8 or even dimmer who work at the Paranal observatory will have given this a try?


texts: Apparent size of the super blue blood moon

texts: Is it normal that super blue blood moon is much smaller than before the eclipse? If so, why? I'm quite positive it's not cloudy here. On my TV, they broadcast a live super blue blood moon from the 4th floor, and it looks big and red. You think they use a telescope?


texts: Are there naturally radiation shielded areas on Mars? (shadowed by terrain formations)

texts: Mars' thin atmosphere and lack of magnetosphere exposes its surface to lots of Solar UV radiation and cosmic radiation. But Mars also has some dramatic altitude gradients in for example Valles Marinaris. Are there any areas which in this way are protected from A) Solar UV radiation and flares and coronal mass ejections, and/or B) substantially protected from cosmic radiation?


texts: Would They Tell Us If An Unstoppable Threat Was Approaching

texts:
This recent piece somewhat kindled my thoughts on this question, but I've pondered it for a while now: https://www.scientificamerican.com/article/a-movie-of-the-evolving-universe-is-potentially-scary/
With the new, more powerful scopes coming online in the coming years, would we be told if they discovered an approaching, world-ending threat? This hypothetical threat could be years, decades or even longer away.
What first made me even consider this was the situation with space shuttle Columbia where, I believe, the crew weren't told about the damaged tiles as there was nothing they could do about it anyway.
So, if the new scopes found a huge asteroid, or maybe even a star that was on course to do fatal damage to us in 10 years or something, and there was currently no way at all stop it, would they tell us?
Would the fear of mass panic stop them from telling us?
Thank you.


texts: The size of Copernicus’ and Ptolemy’s corrections

texts: I understand that both Copernicus and Ptolemy needed epicycles, but one might assume that a heliocentric system would need much smaller corrections to account for the non-circular motion of the planets.  This is however not mentioned as an important reason to favor Copernicus’ system. Is this not the case?


texts:
How different would space have been if there was no dark matter?
Can space be considered vacuum even when occupied with abundant dark matter?


texts: Can tidally locked planets have liquid oceans on their night side, and would such a planet be habitable?

texts:
Let's say we have a tidally locked planet orbiting a star. And let's say that the conditions on its surface are just right for water to exist on its surface. Conventional wisdom says that the water on the day side will be liquid, while the night side will be covered with a sheet of ice.

However, I'm wondering if this is a hard and fast rule. What I want to know is if it is possible for tidally locked worlds to have liquid water persist on its night side, and what conditions could bring this about. And would those conditions still leave the world habitable?


texts: Get date and time by position of the sun and the observer position

texts:
I am working on an astrology project (don't panic, my question is about astronomy or math), where I need to figure out some values by the longnitude of the planets.

I have a program for this, the Swiss ephemeris.

With this, I can get the position of the planets by the time and the geolocation of the observer.

What I need to do is to do it backward, so I need to get the exact date and time by the given position of the sun and the position of the observer.

For example, today (2015.12.16 00:00:00 UT) the longitude of the sun is 263.6893755 from postion (lng,lat,alt) 19.2,47.29,0 on Earth.

I need a formula, what tells me, what was the UT time from this longitude of sun -88 degree.

Can anybody give me a clue, how can I calculate this?

I made some research of course on the net, and I found the related wiki article, but if I am honest, there are too many unknown terms and phrase here, what I really do not understand, and I do not want to dig in too deep.


texts: Software to convert RA and DEC into ALT and AZ

texts:
I have implemented the formulas to convert AR and Dec into altitude and Azimuth in C++ following the book Practical Astronomy with your Calculator or Spreadsheet 4th Edition.

In the book there is an example to check if I have do it fine. This example works perfectly but I want to check if my formulas are correct.

I have use this page to check it but I get different minutes values in both altitude and azimuth values.

I have checked on that page that I get the same LST value, but ALT and AZ have different values. This data I have tested:

Altitude: -15° 27' 40"
Azimuth:  273° 12' 34"

This is the data get it from that page:

Do you know if there is another web page or program to check if the result of my formulas are correct?

UPDATE:
I have tried to get Azimuth and Altitude using a date in year 2000 in web page and my program and this is the result (you can find my program's result at the bottom of the image):

Is this the same problem like the previous one (I'm not taking account for precession)?


texts: What is the 'scale factor' equation for a dark-matter dominated universe?

texts:
The Friedmann equations can be solved exactly in presence of a perfect fluid with equation of state
$${\displaystyle p=w\rho c^{2}} \qquad p=w\rho c^2$$
where ${\displaystyle p}$ is the pressure, ${\displaystyle \rho }$  is the mass density of the fluid in the co-moving frame and $w$ is some constant.
In spatially flat case ($k = 0$), the solution for the scale factor is
$${\displaystyle a(t)=a_{0}\,t^{\frac {2}{3(w+1)}}}$$
where ${\displaystyle a_{0}}$ is some integration constant to be fixed by the choice of initial conditions. This family of solutions labelled by ${\displaystyle w}$ is extremely important for cosmology. E.g. ${\displaystyle w=0}$ describes a matter-dominated universe, where the pressure is negligible with respect to the mass density. From the generic solution one easily sees that in a matter-dominated universe the scale factor goes as
$${\displaystyle a(t)\propto t^{2/3}}$$ matter-dominated
Another important example is the case of a radiation-dominated universe, i.e., when ${\displaystyle w=1/3}$. This leads to
$${\displaystyle a(t)\propto t^{1/2}}$$ radiation dominated
Note that this solution is not valid for domination of the cosmological constant, which corresponds to an ${\displaystyle w=-1}$. In this case the energy density is constant and the scale factor grows exponentially.
So, '$a$' is proportional to $t^{2/3}$ or $t^{1/2}$ for matter- or radiation-dominated universes, respectively... But if '$w$' is negative-one then '$a$' is proportional to $t^t$?
I mean, what is the exponent in this 'exponential growth' phase where the '$w$' 'constant' is $-1$?


texts: Relation between initial mass and evolutionary phases lifetimes

texts:
Consider the following image (Source: An Introduction to Modern Astrophysics):

There seems to be a relation between the initial mass/mass at the beginning of the MS and the time spent during different evolutionary phases.

Is the this relation empirical or can it be quantified?

For example, the MS lifetime is proportional to $M / L$ , I want to know whether a relationship like this exists for other phases.

Edit 1:

See this image for more details, does there exist any quantitative relation from which these values can be obtained?


texts: Photodetector Question: Does converting an RGB image to grayscale produce the same result as using a grayscale image detector?

texts:
FYI my application is not astronomy related, but I know astronomy folks have a lot of knowledge of photodetection and spectrometry instrumentation, so I am seeking this community's help.

I'm interested in doing both spectral and RGB imaging. I'm wondering if I can do both with just an RGB CMOS camera... The way I would approach the spectral imaging is to illuminate my sample with monochromatic light one wavelength at a time and then convert the images to grayscale. Each grayscale image would represent the intensity of light reflecting from my sample at a particular wavelength. I would love for this to work, but I am doubtful that the converted image will actually represent what a grayscale camera would record.

Bit of an odd scenario... Wasn't sure how to search the web for this. Any help is appreciated! Thanks!


texts: What processes does a star undergo to become a pulsar? Does it take a very specific star with a certain set of qualities such as "Just the right mass, diameter, and composition," or is it a freak accident that certain stars live out their remaining life as a pulsar?


texts: Which worlds have unique words for a "day"?

texts:
On Mars, we refer to a "day" as a "sol". NASA has developed a whole vocabulary around this term, like "yestersol" and "tosol", etc.

Do any other worlds have unique terms like this? How would one refer to a day on Venus, for example, or Mercury? Is "sol" used to avoid confusion with "day", like on Mars, or is "sol" an exclusively Martian term and "day" should be used for any other world until a unique term is agreed upon?


texts: Before the 1761 transit, what was our best estimate of the distance to the Sun?

texts:
In 1761, many expeditions were launched to determine the distance to the Sun using parallax during the transit of Venus. Prior to the 1761 transit, what was the best estimate for the Earth-Sun distance?
In antiquity, Aristarchus found that the Earth-Sun distance was 20 times the Earth-Moon distance, which is a very gross underestimate. Were there any better measurements than Aristarchus' measurement in the early 18th century?


texts:
What should I improve my telescope kit to see more details of Moon?
I have the gskyer telescope of 60mm aperture and 350mm focal length.
my eyepieces are 10mm,25mm.
and I have x3 Barlow.
my best viewing of the Moon when I combine the Barlow with 10mm eyepiece.
I want to see deep details of the moon, by the way, this helps me to zoom in more for the planets like Mars, Jupiter, and Saturn.
any help?


texts:
I'm looking for the latest values (with uncertainties) of the four main cosmological density parameters $\Omega_i$ :
\begin{align}\tag{1}
\Omega_{\text{mat}} &={} ?,
&\Omega_{\text{rad}} &={} ?,
&\Omega_{\Lambda} &={} ?,
&\Omega_{k} &={} ?.
\end{align}
I know that $\Omega_{\text{mat}} \approx 0.30$, $\Omega_{\text{rad}} \approx 0.00$, $\Omega_{\Lambda} \approx 0.70$ and $\Omega_{k} \approx 0.00$, but I would like to have more precise values (with uncertainties, if possible).  Take note that these parameters are constrained by the following relation :
\begin{equation}\tag{2}
\Omega_{\text{mat}} + \Omega_{\text{rad}} + \Omega_{\Lambda} + \Omega_{k} \equiv 1.
\end{equation}

Of course, I checked Wikipedia but I don't trust it very much :

https://en.wikipedia.org/wiki/Lambda-CDM_model

I've also checked on arXiv.  For example :

https://arxiv.org/abs/1502.01589,

but I don't find clear final and consensual values in this paper.

Help would be appreciated.  Please state your sources.


texts: Difference in time between sunset and moonrise on a full moon

texts:
So as a Sailor I have experienced some times where sunset and moonrise are very close together (this happens when it's full moon) which is particularly beautiful. I assumed that this was always the case but looking more closely at time difference between sunset and moonrise they can change quite dramatically.

2019 (Porto-Vecchio France)
Date        sunset   moonrise  diff
04/20       20:08    21:24     1:16
05/19       20:39    21:20     0:41
06/18       20:59    22:05     1:06
07/17       20:54    21:31     0:37
08/16       20:21    21:12     0:51

As you can see there is some degree of variation, can someone explain why this happens and how I can find out where and when they are closest together?


texts: Stars that don't fit $L=4\pi R^{2}\sigma T^{4}$?

texts:
When calculating luminosity/radius/temperature for several stars, I've noticed that while the majority of stars conform to the luminosity relationship $L=4\pi R^{2}\sigma T^{4}$, there are a few that don't. Take 8 Ursae Minoris. As far as I can tell it has a luminosity 56 times that of the sun, a radius of 8.5 solar radii and an effective temperature of about 5000 K. When I substitute those numbers in they don't match. The math isn't wrong so I can only assume either the data isn't reliable, or maybe there is a certain class of stars that don't conform to that relation. I don't know enough astronomy to determine which is correct, but I suspect obtaining a reliable luminosity value for some stars could be the problem.

Does anyone know the answer to this riddle?


texts: How is information preserved on the surface of a Black Hole?

texts:
Is there an compression algorithm for storing the information?

What if there is a uniformaly complex object dropped to the black hole? Then there will be no compression of information.

How is there enough space on the surface (2D) to encode something which is in 3D. The planck distance is the same in the black hole as in the universe. So how can the black hole encode information about an object in 3D that is both uniformly complex and as dense as the black hole? Or is there a law that says 3D objects cannot be more dense then some level - which is sufficiently sparse so that when collapsed to a black hole all its information can be encoded on the surface of a sphere? Has this limit been found - given that a sphere has the lowest surface to volume of any object: https://en.wikipedia.org/wiki/Surface-area-to-volume_ratio ?

Edit: added '3D' to first sentence of 2. question.


texts: How do we differentiate between a star or planet and noise introduced due to equipment?

texts:
I understand that differentiating between celestial bodies and noise due to equipment is a fundamental problem in astronomy. I also understand that we solve this problem by looking at something called flux density and continuum and line spectra but how do I understand these terms ??
Please consider I'm well versed in university level physics so I understand how spectra will help but don't understand which quantity's flux density do we look for in astronomy. Please help me understand these terms and hence solve the noise vs star/planet problem.


texts: Less stars in the night, compared to 15-20 years back

texts:
I am not sure if my question is true or not. But this is what I observe regularly. When I was young and when I look at the sky, there were too many many stars were there. But now, from few months I'm observing the sky (by eyes, not any telescope), I see very few stars. Perhaps, countable.

Is it because:

Stars are dead? (Not all) As I read somewhere, by the time you see the star, it would have been dead. Because, the light would've traveled so many years to reach earth. By the time, star would have completed 'X' light years and it is dead by now?
Current position of the earth in galaxy: As I read, the earth will not always traverse in the same path around the sun. So the current view from the earth to the sky, may not have any star? (This is my guess/imagination, I'm not sure)
Is it because of the city light/ pollution?

PS: Please be easy. May be the question is broad or simple, just want to know the brief answer and if its complete explanatory, I'm happy for that.


texts: Ejected planets during the early stages of the formation of the Solar System

texts:
This is similar to a previously asked question, but I am just asking about theory rather than observational evidence. Assuming there were a much larger number of protoplanets in the early Solar System, what percentage of these would theoretically have been ejected (orbital velocity increased beyond escape velocity due to interaction) and what percentage would have been just moved out to a more distant orbit (say, in the Kuiper Belt or the Oort Cloud)?
In other words, should we expect to find rocky worlds in the far outer Solar System that were formed inside the current radius of the asteroid belt?


texts: Why are there no ISM clouds with temperatures between 100 and 6,000K?

texts:
In the interstellar medium, there are several different diffuse phases of gas, distinguished by their density and temperature. Specifically, the cold neutral medium has temperatures from ~50-100 K and the warm neutral medium ranges from 6,000-10,000 K. According to my professor, there have been few gas clouds found with temperatures between these two.

Does anyone know why such a large gap exists?


texts: What methods can high school students use to measure the radius of the earth?

texts:
I suppose they could split into 2 groups and use the shadow method from different latitudes.

Maybe they could also use the stars on the horizon at two different latitudes.

Is measuring a ship below the horizon feasible ?

What other methods could be tried by high school students?


texts: How do elements with only one shell emit light?

texts: Electrons move to higher energy levels and drop back (electron migration). When they drop levels, photons are emitted and the wavelength/frequency emitted is based on how many levels are dropped. My question is, how does this work with elements with only one shell, such as hydrogen? Also, what determines how many energy levels are dropped?


texts:
I'm using a 95mm f/8.4 telescope. What's the best eyepiece that I can buy for a very close look at the moon or even planets? I'm a beginner in this field so please help me.
Thank you.


texts: Why is it that we can"t feel how fast the Earth is moving?

texts: We are moving like 100,000 mph. And why do we not fall off going that fast


texts: Sky from Equator at 8,000 years Before Present?

texts: The Stellarium software allows future views of the sky. I need an online resource (planetarium projector?) that shows pre-historical views, and from the Equator at 8,000 years before the present.


texts: Why is there so much excitement over helium having been discovered on an exoplanet? Isn't it oxygen that we should be looking for, since this is what is needed for life? What do we need helium for?


texts:
Currently we observe that the universe is expanding. And this expansion even goes faster and faster.

Why do we know (or presume) that this expansion started slowly at a singularity (i.e. big bang) and is getting faster and faster?

Did a serious scientist ever presumed that the universe might be oscillating, i.e. like a breathing bubble? Currently the universe is expanding but who knows, perhaps in 1 Million year we will observe a shrinking universe and 3 Million year later again expanding - provided the humans will still exist at this time which I doubt.

Of course, this would open many new questions like: How and when did it start? What is the frequency and amplitude? But let's keep this question off side.


texts: Measurement precision of celestial events

texts:
The local weatherman declared that fall starts at exactly 10:21am (local time). Ignoring the fact that seasonal boundaries have multiple definitions (meteorological, astronomical, etc.), what he perhaps means to have said is that the fall equinox occurs at that moment.

Presumably, that is the moment at which Earth's axis of rotation is exactly perpendicular to the Sun-Earth line.

My question is: to what degree of precision can this be measured? The weatherman's statement was to the minute. But is it actually measured to a finer precision? If so, plus or minus how many seconds?

What about the the solstices? Can they be measured to the same degree of accuracy? Are there factors which uniquely affect the accuracy of either measurement?


texts: Recently, I answered this question and need some clarification regarding the gravity when within the radius of a star. I thought that, when something is inside a star (ignoring drag), it will experience less gravity because as it goes deeper inside, more and more mass is outside (in the up direction) the distance left before it reaches the center. Is this true, and is there a formula that needs certain parameters to calculate it?


texts: New Horizons, speediest yet, is currently running at about 15 km/sec relative to the sun.  What is the roadmap for future ? How is it possible to reach much faster speeds ?


texts: Is blue light not traveling faster then red light in space?

texts:
I just can't understand why light and other massless particles are not traveling at different speeds?

Gravity effects anything with a mass but light has no mass but a black hole, and weak lensing changes the trajectory of light to create more red shifted light more than blue shifted light. That tells me light has mass. Can someone clarify this to me in Laymons terminology?
Pictures would be helpful.


texts: What fraction of galaxies host active galactic nuclei?

texts:
I've been saying "some". I can't find a reference for a particular percentage.

This seems to address the question to some extent; https://arxiv.org/abs/astro-ph/0108389 would "roughly 1%" be in the right ballpark for an answer then?

pesa points out this is redshift-dependent. I am looking for a ballpark figure of the fraction of AGN at $z < 1$.


texts: What do astronomers do different now that they know about fusion of the Sun?

texts: I would like to know how knowledge of the fusion in the Sun has changed how astronomers explore the universe. What do astronomers do differently now that we know that the Sun’s use of proton-to-proton chain to create energy? Please include sources.


texts: How fast does Venus move as seen from the earth?

texts:
So last night I was about to sleep with the window in front of me. there was a 3 inch gap between the curtains that let me see a small portion of the sky. I could see something magnificently bright in the sky that couldn't be anything but Venus. So while I was looking at it for about 1-2 minutes it gradually moved out of my sight. That seemed pretty fast. I mean I kinda estimated that with such a speed it could move from east to west in less than 2 hours.
So is that normal?


texts: Exactly how elliptical is Mercury's orbit, visually, without exaggeration?

texts:
Reposting question from https://www.reddit.com/r/askscience/comments/5e1zhy/what_does_mercurys_orbit_really_look_like/ which reads:

  First the full question: What does the orbit of Mercury really look
  like visually, without artistic liberties taken to amplify the
  eccentricity of the orbit, or simplifying it to appear as a perfect
  circle? What eccentricities are needed for orbits that readily appear
  elliptical?

I originally did this as a self-answer, but my answer was of such poor quality I've now deleted it. I hope to do a better answer backed by some calculations, but, as always, anyone else is free to answer.


texts:
Exactly what is the non-thermal Sunyaev-Zel'dovich effect? From what I understand from reading several papers by Mark Birkinshaw and Sergio Colafrancesco, I get the rough idea that the non-thermal SZ effect has something to do with it being in the relativistic realm.

Papers by Sergio Colafrancesco:

Polarization of the Sunyaev-Zel'dovich effect: relativistic imprint of thermal and non-thermal plasma
The non-thermal Sunyaev-Zel'dovich effect in clusters of galaxies
Non-thermal phenomena in galaxy clusters: cosmological relevance

Review by Mark Birkinshaw:

The Sunyaev-Zel'dovich effect

To clarify, I'm not referring to the kinematic SZ effect.

There appears to be a distinction by the authors between the SZ effect due to hot thermal electrons and relativistic electrons. I find the nomenclature ambiguous, as temperature is essentially kinetic energy on a smaller scale, so why would relativistic electrons that have more kinetic energy be 'non-thermal'?

Lastly, is the key distinction between them using a relativistic vs. a non-relativistic formulation?


texts: How fast stars accelerating away from a central point? Are they increasing in acceleration or decreasing? If possible could you please provide a plot of the acceleration of stars away from the central fixed point.


texts: I, like many others, am excited to see the eclipse. I want to view the eclipse through my telescope, however, I don't have any solar safety equipment for solar viewing and I cannot find any online that I can get before the eclipse. Could anyone lead me to a reputable site where I could purchase solar (preferably mylar) film before the eclipse?


texts:
I originally went to math.stackexchange.com and they suggested I try here as well.

I'm trying to figure out how to calculate times of moonrise and moonset for a given position on the earth on a particular date. I'm using Vallado's Fundamentals of Astrodynamics and Applications because there is an example in the book that lays out a simplified process. I'm stuck at the point where I'm trying to calculate Longitude of the ecliptic for the Moon. The formula is below where T = -0.013634497.

  λEcliptic = 218.32° + 481,267.8813T + 6.29Sin(134.9 + 477,198.85T) - 1.27Sin(259.2 - 413,335.38T) + 0.66Sin(235.7 + 890,534.23T) + 0.21Sin(269.9 + 954,397.70T) - 0.19Sin(357.5 + 35,999.05T) - 0.11Sin(186.6 + 966,404.05T)

The expected answer is -0.8412457°. However, I'm unable to figure out how to get this answer. My calculations are below:

  1) 218.32° + 481,267.8813T = -6343.525

  2) 6.29Sin(134.9 + 477,198.85T) = 5.963779

  3) -1.27Sin(259.2 - 413,335.38T) = -0.900843

  4) 0.66Sin(235.7 + 890,534.23T) = -0.292285

  5) 0.21Sin(269.9 + 954,397.70T) = -0.126871

  6) -0.19Sin(357.5 + 35,999.05T) = 0.138211

  7) -0.11Sin(186.6 + 966,404.05T) = 0.054722

Simply adding or subtracting gets me -6338.688731. How can I get the value -0.8412457° from this. My trigonometry is rusty and I'm not sure how to get the right answer. Any help would be greatly appreciated. Thanks.


texts: mm-wavelengths Moon map, scientific case

texts:
I would like to test a telescope with a Moon observation.
It is a low spectrometer-imager at 110-300 GHz with a resolution of 4 arcmin@150 GHz.

Is there any scientific target that concerns the Moon with such an observation?


texts: Does anybody know date of publishing of following spirit rover image in NASA apod?

texts:
I want to find this image in the following linked index.
https://apod.nasa.gov/apod/archivepix.html


texts: How often do partial solar eclipses of 90% of totality occur in same place?

texts:
I know that the mean interval between total eclipses in a single place is about 375 years, which is not surprising given the small band of area of the totality. However, the penumbra of the eclipse partially shadows a much larger area than the totality:

Image Credit: NASA Scientific Visualization Studio

If we were to take a wider area, such as the band of 90% coverage, how many years would there be between eclipses at a single place on average?


texts: Do astronomers have any idea what percentage of our galaxy’s stars move in retrograde orbits?

texts:
I recently noticed that none of the planets in our solar system orbit the Sun in a retrograde direction. This is likely because they formed moving in the same direction as the planetary disk did in respect to the Sun.

Are there stars that move retrograde to the Milky Way galaxy's rotation? If so, where are they concentrated, and why?


texts: How do you calculate local time from local sidereal time?

texts:
There are many calculators online to convert local time to local sidereal time, but I can't find any resources to convert the other way.  Can you convert back by doing the same conversion backwards?  I found equations on this website to convert to LST.  Would it be valid to use this equation to convert back:

$$
UT = \frac{LST - \frac{L}{15} - 6.697374558 - 2400.051336*T - 0.000025862*T^2)}{1.0027379093}
$$

where $UT$ is the time in Universal Coordinated Time, $LST$ is the Local Sidereal Time, $L$ is the longitude, and $T$ is:

$$
T = \frac{JD-2451545.0}{36525.0}
$$
where JD is the Julian Date at noon UTC.  Once I've calculated the time in UT, I then add or subtract 24 until the result is within 0 - 24 hours.  Then I can convert from UT to local time.

I would prefer to have this as accurate as possible.  I did a calculation using this, but according to Stellarium I was off by about an hour.  Could this be due to Daylight Savings time or something?

Here is the Python code I made to do the calculation.

LST = 8 + ((37 + (5.642/60))/60)
JD0 = 2457813.5
L = - 106.6056
GMST = LST - L/(365/(23 + ((56 + (4.1/60))/60)))
T = (JD0 - 2451545)/36525
UT = (GMST - 6.697374558 - 2400.051336*T - 0.000025862*(T*T))/1.0027379093

while UT <0:
    UT += 24

LT = UT - 7

while LT < 0:
    LT += 24


texts: Why did it take five years to "figure out" how to use astrometric calibration sources to deblur LOFAR images?

texts:
Quanta Magazine's The Hidden Magnetic Universe Begins to Come Into View is a fascinating review of a rapidly evolving field in astronomy.
It contains some statements:

In their paper last year, van Weeren and 28 co-authors inferred the presence of a magnetic field in the filament between galaxy clusters Abell 399 and Abell 401 from the way the field redirects high-speed electrons and other charged particles passing through it. As their paths twist in the field, these charged particles release faint “synchrotron radiation.”
The synchrotron signal is strongest at low radio frequencies, making it ripe for detection by LOFAR, an array of 20,000 low-frequency radio antennas spread across Europe.
The team actually gathered data from the filament back in 2014 during a single eight-hour stretch, but the data sat waiting as the radio astronomy community spent years figuring out how to improve the calibration of LOFAR’s measurements. Earth’s atmosphere refracts radio waves that pass through it, so LOFAR views the cosmos as if from the bottom of a swimming pool. The researchers solved the problem by tracking the wobble of “beacons” in the sky — radio emitters with precisely known locations — and correcting for this wobble to deblur all the data. When they applied the deblurring algorithm to data from the filament, they saw the glow of synchrotron emissions right away.

The filament between galaxy clusters Abell 399 and Abell 401 is also discussed in How is it determined that the X-ray and radio intensity come from a magnetic field bridge between two clusters of galaxies?
Question: Why exactly did it take five years for the radio astronomy community to "figure out" how to improve  the calibration these LOFAR measurements and apply deblurring algorithms? Answers to

Would Adaptive Optics be Useful in Radio Astronomy?
What is precipitable water vapor in millimeter-wave radioastronomy and how is it measured?
What can be learned from low frequency radio astronomy available outside of Earth's ionosphere?
In the 1950's how were radio-astrometric positions with portable dishes so precise they could be assigned to their dim optical counterparts (Quasars)?
What exactly is interplanetary scintillation; what was the Interplanetary Scintillation Array looking for? Did it successfully observe any?

suggest that correcting for spatial variations in water vapor or other effects is a known thing in radio astronomy. However discussions at How large does refraction become in radioastronomy? suggest that the ionosphere becomes increasingly important at low frequency (the "LOF" in LOFAR) so perhaps this was part of the challenge?


texts: Are the stars outside of the galactic plane in the galactic halo?

texts: The majority of the stars we see in the sky, like Pollux, are outside of the galactic plane. That means that all those stars we see are not in the galactic disk, and therefore are in the galactic halo, whereas Capella, for example, is where?


texts: Could this estimate of the size and mass of the Chicxulub Impactor be accurate?

texts: My understanding has always been that the Chicxulub Impactor was in all likelihood an asteroid with a diameter of about 8 - 12 km, but then, the other day, I came across this paper. In it, they say that the diameter of the impactor could have been as large as 81(!) km, and that it was probably a comet and not an asteroid, a claim they base on the amount of iridium found in the layer associated with the impact. I'm not an astronomer so I'm not really in a position to evaluate the veracity of their claims and how they arrived at them, which is why I'm wondering if what they say could plausibly have been the case?


texts: Does the dimming of Betelgeuse present any observational opportunities?

texts:
Recent photometry suggests that Betelgeuse has been dimming over the past three or so months, reaching the faintest V-band magnitude seen in modern observations. The changes are apparently even visible to the naked eye, and appear to correspond to a temperature drop of $\sim$150 K relative to maximum brightness. The second Astronomer's Telegram on the phenomenon ends with

  This continues to be an opportune time to carry out complementary measures of Betelgeuse while it is in its current low state and is unusually cool and faint.

This got me thinking. Obviously, continuing photometry will tell us more about the dimming itself. However, regardless of the mechanism behind the phenomenon, is there anything we can glean from the dimming about the star itself - e.g. composition, rotation, limb darkening, etc. - and its circumstellar environment (e.g. a binary companion, which I assume is unlikely, or circumstellar dust)?

Essentially, are there any observations of Betelgeuse that would be made easier by the recent changes? Or am I being overly naïve, and they're really too minor to be of any use?


texts:
Main question: Could dark energy (the mysterious accelerating expansion of the universe) be explained by "negative gravity"?

"Spin off" questions:

Does antimatter have negative gravity?
If antimatter has negative gravity, and is present in the universe with equal amounts of matter and antimatter, would it produce the observed amount of dark energy in the universe?

My theory that I am trying to validate:

Gravity is the flow of space into matter, and it flows out of antimatter.  If this is true, antimatter should have "negative gravity", I would expect it to have a repelling effect, while matter has an attracting effect.  For example, if antimatter were on earth (somehow without annihilating), it would fall to the planet.  However, if there were an antimatter planet, objects would "fall up" off it.  In fact, I believe the antimatter planet would break apart because of this quality.  Furthermore, I don't believe antimatter planets or stars would form because of this quality (e.g. it would remain anti-hydrogen).  I also theorize that it would be in parts of the universe where matter isn't (e.g. in the voids outside the galactic clusters), and would be very diffuse (because it would repel itself).  I believe the theorized repelling effect of antimatter could be what we are observing as dark energy (hence why I am asking these questions).  I just searched for this online to see if anyone else has this theory, and yes, someone has something very similar here: http://www.universetoday.com/84934/antigravity-could-replace-dark-energy-as-cause-of-universes-expansion/

** Edit **

It seems others have caught on and simulated the idea of negative mass as dark energy in the universe.  They have run simulations with equal mass and negative mass and ended up with a result that resembles the current universe!  They say negative mass might also explain dark matter!  Check it out here: https://youtu.be/MZtS7cBMIc4

This video also shows how negative mass might react: https://youtu.be/uAJlg8MDAlU


texts: Can telescopes determine whether Hygiea is in hydrostatic equilibrium?

texts:
10 Hygiea is a spherical body in the main asteroid belt. With future telescopes like the Vera Rubin LSST or the James Webb Space Telescope, can we determine whether Hygiea is actually in hydrostatic equilibrium, or do we have to send a probe? For the IAU to classify a body a planet or "dwarf planet" it must currently be in hydrostatic equilibrium. Could we (dis-)prove that on Hygiea with the telescopes to come?
Does really nobody know? I suppose the answer is "they might determine it" then?


texts: What defines the plane of an accretion disk around a black hole?

texts:
The question Do we know at which angle the Event Horizon Telescope will look at the accretion disk of Sagittarius A*? about just how close to edge-on we would be viewing any accretion disk around the black hole in the center of our galaxy, and @Zephyr's excellent answer have got be thinking about the geometry and angular momentum.

While the angular momentum vector of a black hole will likely reflect that of all the matter that fell into it , would the plane of any accretion disk around a black hole reflect the black hole's current equatorial plane, or a plane defined by rotation of whatever material is currently falling in to it?

Another way to formulate this question might be to propose an incredibly unlikely Gedankenexperiment. If I inserted a black hole into the center of a rotating disk of material so that the black hole's axis was in the plane of the disk of material rather than parallel to its rotational axis, would a well-defined accretion disk form all all, and if so, what would determine the orientation of that plane?


texts: How do they know the TNT equivalent of the meteor explosion over Vermont?

texts:
I've seen several reports of this meteor explosion, below are two.
Was there infrasound recordings of the pressure wave, or were weak, local seismic signals recorded, or it this just a ballpark estimate based on circumstantial evidence?

Bangor Daily News: Meteor exploded over Vermont with force of 440 pounds of TNT
Sputnik News: Yield of Fireball Explosion Above Vermont Rated at 200 Kilo(grams) of TNT - Video


texts: What name was voted for Tau Boötis b by the Name Exoworlds Project?

texts:
In 2015, the exoplanet Tau Boötis b was included in the  Name Exoworlds Project, a project where various international astronomy organizations would propose names for a selection of known exoplanets that complied with a set of guidelines presented by the International Astronomical Union. Upon completion of submissions, voting was opened to the public, with the selected and approved names being published.
The IAU decided that the name voted for Tau Boötis b did not not meet the naming guidelines, and annulled the result of the vote.
I have no objection to them deciding to not use the name, and  I don't want this to be come an argument as to whether they should have annulled it. I just want to know: has it ever been revealed what the public-voted name was, and if non-obvious, the reason it was annulled?


texts: Secondary maximum in SNIa lightcurves for near infrared

texts:
Type Ia supernovae (SNIa) are thermonuclear supernovae that generates a lot of Nickel 56 which emits photons while disintegrating.

How is the secondary maximum in lightcurves for reddish bands (see I, J, H, K bands in the figure below) explained ?


texts: Are there any predictions of what galaxies exist in the Norma cluster/ Abell 3267?

texts:
I am working on a map for a science fiction story and using what information is available I have a good idea of locations of nearby galaxy groups and clusters and where the known supermassive black holes are.
As the Norma cluster is a big area of debate and due to that and other areas being obscured by our own galaxies, observing what is in those areas is difficult. Going off Wikipedia this cluster has a binding mass of 1E15 solar masses, which is the same as the Virgo cluster and only one galaxy is mentioned which is ESO 137-001.
Is this mass based of our galaxies motion in that direction so mass behind the cluster (some believe the Shapley supercluster) is giving the value we have or is that a known mass of galaxies in that cluster? If so can we predict if it has a similar number of large galaxies and supermassive black holes as the Virgo cluster or is there other predictions for the Norma cluster?


texts: Can a tectonically inactive planet retain a long-term atmosphere?

texts:
Can a planet be tectonically inactive and still retain a magnetosphere and protected atmosphere? How does that work?

How else could a planet retain a thick atmosphere like Earth's for extensive periods of time?

Note, I'm not asking on Earth science SE as, well, the question is not about Earth. I was hoping there was some sort of astronomical theory for other potential habitable planets.


texts: Why don't black holes quickly eat up the galaxy/universe?

texts:
It's my understanding that the radius of the event horizon of a black hole is proportional to it's mass.
Which means the surface area of a black hole is proportional to it's mass squared.
Lets just assume that black holes eat stuff that by chance "runs into them".
Using this (perhaps naive) assumption, this would mean black holes gain mass at a rate proportional to their surface area, which is the same as their radius squared, which is their mass squared.
So then we get something like:
$\frac{dm}{dt} \propto m^2$
$m = 1 / (C - t)$
Which means that all black holes should grow to an infinite size in a finite length of time.
Indeed they will eventually get to a point where even small amounts of mass will grow the volume of the black hole so much (because volume increase is proportional to the current mass squared) and even if the density of the universe is very low this will eventually mean any growth will set off runaway growth because each atom the black hole swallows increases it's volume such that on average that new volume contains a new atom.
Is it just that the constant factors here are very high, or are one of my assumption quite incorrect? I say quite incorrect because even if they're slightly incorrect (the growth rate is proportional to mass not mass squared) many of these issues still occur on long enough timescales.


texts: Quadrantids Meteor Shower 2020 viewing times

texts:
It's my first time going to see the Quadrantids Meteor Shower, or any meteor shower in fact. I just want to know if I'm getting the right info for viewing this event. I got my info from this site Timeanddate.com. My location is Penang, Malaysia. Peak time: 5th Jan 2020

To my knowledge,

I won't be able to witness the event earlier than 4am because the position of the radiant is below the horizon.
I will need to be at a dark area (using this as a guide)
I will need to be facing 32-41 degrees northeast of True North. For this I will be using Google Maps instead of a compass because compass is magnetic North?
I will need to look for it at 6 to 33 degrees above horizon (depending on the time)
A local article such as this can't be trusted because it says you can view it from 11pm (there are many sites other local sites claiming you can see the event starting from 11pm)

Good to go?


texts: After Oumuamua passage, has an "urgency" telescope time request procedure been set up?

texts:
During the rapid passing of ʻOumuamua through our solar system, it was difficult to get instant telescope time. Usually, formal requests and a review process are necessary before telescope time is provided to a particular project.

Now everybody is excited and eager to observe more interstellar objects. Did "they" set up an appropriate request procedure for immediate telescope usage for that matter? Or can one expect that similar hurdles and paperwork are required when the next such object is discovered?

Is there any kind of international standard, or are such requests managed individually by each observatory?


texts: I made a graph trying to show the Sun's movement relative to the Galactic Plane. It doesn't seem to be correct

texts: I made a Desmos Graph following the most voted answer of this question, but I'm not sure if it is correct, because it suggest that the formation of the Sun happened shortly after it would have crossed the galactic plane, but the Sun did not exist before that. Is that possible?


texts: How much infrared radiation is emitted by a bow shock?

texts:
Has the amount of energy being emitted from R Hydrae's bow shock been studied?

If so, is there any information how much infrared radiation is emitted in any means of measurement?

If the infrared energy from the Sun, measured 1 AU from the Sun being approximately 680 watts per meter square, how would the infrared energy of the bow shock compare at the same distance measured in the same units?

Thanks to AtmosphericPrisonEscape for pointing me in the right direction.  I found this table from the DETECTION OF A FAR-INFRARED BOW SHOCK NEBULA AROUND R HYA: THE FIRST MIRIAD RESULTS.

with the CSEs being the circumstellar envelopes.  Does this mean the CSE (bow shock?) is about 57% (19.7 compared to 33.9) the flux of the star at the 70 microns (mosaic) band?


texts: Which is the farthest distance a particular distant known- identified object from the asteroid belt can get from the sun?

texts:
According to

Space facts

  The Asteroid Belt is located in an area of space between the orbits of
  Mars and Jupiter. That places it between 2.2 and 3.2 astronomical
  units (AU) from the Sun

But asteroids from the asteroid Velt like Pallas and Hygiea have an aphelion of
3.4119 AU and 3.5024 AU respectively. So my question is, which is the farthest distance a particular distant known-identified object from the asteroid belt can get from the sun?

Updated since the question might seem unclear. I'm asking for a currently known object from the asteroid belt which gets closer to Jupiter.


texts: Question about the Figure-eight periodic planar three-body motion

texts: If this is a posible periodic solution for a three-body problem, can anybody tell me where is the center of mass of the system? As we know, in a n-body problem the bodies orbit around their center of mass, but here I don't know where it is. Can anybody help me? Thanks.


texts:
If we consider the two largest masses in our solar system - the Sun and Jupiter, by themselves, they will orbit a common barycenter which is somewhere offset from the Sun's center in the direction of Jupiter (just above the Sun's surface). If we add Saturn, things get more complicated, but there is still a barycenter, even if it follows a complex path with respect to the Sun's center (or the Sun has a complex wobble around the barycenter). Add Neptune and all the other masses in the solar system, and things get even more complicated. Neverthess, there is still a barycenter (often outside the limb of the Sun) about which the Sun does a complex dance.

Now, what is Earth actually orbiting? The Earth's orbit is described to be an ellipse; the "center" of an elliptical orbit occurs at one of the focal points of the ellipse. What is at the focal point of the elliptical path the Earth follows? Is it the solar system barycenter or is it the Sun's (wobbling) center of mass? In other words, is the Earth's orbit shifting as the Sun is tugged around, our distance from the Sun never varying by more than the eccentricity of the ellipse, or do we orbit the solar system barycenter, and our distance from the Sun varies by the sum of our orbital eccentricity plus the amount the Sun wobbles in its own orbit around the barycenter?


texts:
Many asteroids are today known to be binary, to have "moons".

But what comets are known to be binary? Or what fraction of them are theoretically thought to be binary? And if possible, then separate Oort cloud comets from comets with more local asteroid like orbits in this respect.


texts: If I were to point into the sky, how many galaxies would be in this line?

texts:
If I point in the sky and draw a line from the tip of my finger to the end of the universe, how many galaxies would this line cross? I had a discussion with my dad and he said due to the universe being so empty the line wouldn't cross any solid matter. I said that the universe is so enormous in size that there would be many galaxies and stars crossing the line.
Is this calculable? If yes which one is correct?


texts:
I am researching about the radius of a star and a its surface area. One question I have is about the effect of changing radii in stars. If for example we have one star with radius $r$ and another one with radius $2r$, we know that the area would mathematically be $A$ for the first star and $4A$ for the second star since $A=4 \pi r^2$. However, I intuitively think that this wouldn't be the case since if I doubled the radius, the surface area will quadruple. But, that means that there will be more molecules and whatever 'materials' the star is made of, meaning that there would be a greater gravitational force towards the core of the star. Would it thus make sense to say that there would be some sort of 'compression' that occurs which pulls all of this extra mass towards the center (effectively making the star denser), and thus the star with $2r$ actually has a surface area of $3\frac{1}{2}A$ rather than $4A$?

(So technically I'm asking if $A\neq 4\pi r ^2$ in case of stars because more mass (due to the extra radius) would mean that the gravitational force towards the core would be greater, making the star denser in the process, but also have less surface area than what doubling the radius would mathematically correspond to.)


texts: Time-frame regarding cosmic expansion and the bound state of the Virgo Cluster

texts:
Due to accelerating cosmic inflation, other galaxies and galaxy clusters will eventually race toward the Hubble horizon apparently away from us, placing them effectively out of our sphere of influence. Due to Virgocentric flow, nearby galaxies, including our own, may become gravitationally bound to the Virgo Supercluster, resisting cosmic expansion (for at least some time).

My question is, Is there any hypothetical time-frame for when this event happens? That is, in what supposed number of billions or trillions of years will the Virgo Supercluster become the only region within the Hubble sphere with which we may interact with?

Edit: Is such an estimate currently impossible? I know I've read one in the past, I just don't remember it well. Somewhen in the ballpark of a trillion years. All I'm looking for is an educated guess.


texts: What causes Titan a moon to have a denser atmosphere than that of a Mars?

texts:
I'm wondering about Mars and Titan. If Mars is larger than Titan how come it lost most of its atmosphere? Mars also has a magnetic field while Titan doesn't. Yet Titans atmospheric pressure on the surface is a whopping 1.5 times that of Earth's.

Question: What causes Mars not to have much of an atmosphere, but Titan does?


texts:
I've got a few questions about the first stars to form in the universe. First off how might metalicity have impacted the formation of the first stars and also what effect would the absence of metals impacted the evolution of these stars?
Why were these stars able to be so massive? I've heard that metallicity impacts opacity so would this maybe inhibit mass loss from radiation pressure?
Would the Eddington limit come into play with stars these large?


texts: What is the lower limit of a coronal mass ejection?

texts:
Reading an 2005 article by Fraser Cain called Smallest Ever Coronal Mass Ejection
 I became interesting in the exact definition of CME.
It seems like a simple question - but I did not manage to find the answer to the question myself. Is there a smallest possible coronal mass ejection (CME)? Is there a theoretical limit or is it a matter of observing capabilities?
Note: I left intentionally open whether "small" refers to mass, size, duration, or any other parameter.
The above mentioned article claims that the CME in the square in the following picture is actually the smallest CME:

Related

Solar Orbiter images first coronal mass ejections, Press release of the Max Planck Institute for Solar System Research, dated May 17, 2021
Wilson effect: How "deep" are sunspots?


texts: Difference of sunset and sunrise of two cities are different

texts:
For 26 Nov 2016:

Consider Tehran with 06:51 sunrise and 16:52 sunset.
Another city is Rafsanjan in 850KM southeast of Tehran, sunrise is 6:21 and 16:45 for sunset.

Time zone of two cities is +3.5

Why difference of sunrise is 30 minutes while sunset is 7 minutes?


texts: Fraction of initial mass lost (radiated) by neutron star mergers compared to black hole mergers?

texts:
GW190521 black hole merger total mass calculation and missing mass, how does this happen? notes that there are about 9 solar masses missing from the final black hole.
GW170817 is the first observed merger of two neutron stars, detected in several ways including a weak gravitational wave.
Do neutron star mergers also radiate several percent of their mass as gravitational waves, or is the fraction much smaller. They comprise ordinary matter rather than being singularities in spacetime, so my guess is that the fraction is much smaller, but I have no idea.
My question is motivated by this answer.

Related:

"Who saw" the binary neutron star merger first? What was the sequence of events? (GRB/GW170817)
What does "GPU-accelerated butterfly matched filtering over dense bank of time-symmetric chirp-like templates" mean? (GW170817)


texts:
After my observation today at the Skytree in Tokyo, I am wondering if this building could be used as a giant sundial?

As an aside, it would be interesting to consider how the Skytree might be used to display the time.


texts: What if a planet or another star or ¨sun¨ collided with our sun?

texts:
Stellar collisions are a well-studied phenomenon in Astronomy, albeit mostly theoretically. In some cases the merger of two low-mass stars can result in a new star plus new planets around it.
But what if a planet (perhaps rogue planet on a grazing hyperbolic orbit, or a large fragment after a planetary collision, or some other mechanism) were to go into a star like our Sun? Would the extreme heat cause the planet to explode (as a hot glass beaker would if you exposed it to cold water) and send lava hurtling towards our beloved earth, or would our sun eat up the planet and get a little bit bigger?


texts: Can one approximate the semi-major axis of an orbit as the average orbital distance for eccentric orbits?

texts:
Kepler's 3rd Law (regarding the relation between orbital period and the semi-major axis of an orbit) applies to all elliptical orbits. But as I understand it, the only reason it is safe to use the approximation that the semi-major axis of an orbit is approximately equal to the average orbital distance is because the planets of our solar system are generally not very eccentric.

As an example, the Earth is about 1 AU away from the Sun and has a very low orbital eccentricity, so one can say that the semi-major axis of the Earth's orbit is also approximately 1 AU in length. Since P^2 (yr) = a^3 (AU), one can deduce that the orbit of Earth should take about a year. But, what if the Earth had a higher eccentricity - If the orbital eccentricity of the Earth were higher, would it still be wise to approximate the orbital distance as the semi-major axis of an orbit?


texts: Searching for stars with a given surface temperature and an absolute magnitude?

texts:
Do you have in mind any database/sites that I can search for stars that matches a given surface temperature and an absolute magnitude?

For example, when I enter Temperature=9,500K & AbsoluteMagnitude=0.58 then the search engine returns the result Vega and some other stars.

Any suggestions are appreciated!


texts:
I just tried to read the new New York Times article Two Black Holes Colliding Not Enough? Make It Three which links to the new 25-June-2020 Physical Review Letter Graham et al. Candidate Electromagnetic Counterpart to the Binary Black Hole Merger Gravitational-Wave Event S190521g
The event described is the merger of two black holes that were embedded in the accretion disk of a supermassive black hole in the center of a galaxy; i.e. in a quasar (loosely speaking).
The NYTimes article describes the following

In the story that Dr. Graham and his team patched together, the black holes were spinning, which caused a recoil that shot the merged result almost straight up and eventually out of the accretion disk at 120 miles per second, at which point the flare stopped. If the explanation is accurate, the black hole should fall back into the accretion disk at the same speed in a few months or a year, generating another flare. “We’ll be looking for that,” Dr. Graham said.

Question: Why would the merger of spinning black holes within the accretion disk of a supermassive black hole cause them to "shoot straight up" out of the disk? How was momentum conserved, i.e. did something else recoil and "shoot straight down"?


texts: Will the night sky ever be more stars than darkness?

texts: Given enough time, will enough light from distant stars reach Earth so that our night sky will be more than 50% stars?


texts: Observed data: Why so many MPECs about TNOs lately?

texts:
The Minor Planet Electronic Circulars (MPECs)
for July 15 through July 18 reported an unusually high number of re-observations of known trans-Neptunian objects (TNOs).
These were found in the
Pan-STARRS archive;
most had not otherwise been observed since discovery.
Is this activity part of the search for Planet 9,
another observing program such as OSSOS,
a result of software improvements,
or just someone clearing a backlog?


texts: What causes the aurora of other planets to have different colors?

texts: All I could come up with is it depends on the atmospheric composition of the planet as they will interact with the charged solar particles which might be true but is there is there a definite reason behind the different colors of aurorae on other worlds (Saturn's blue aurora for example)?


texts:
I noticed that the atmospheres of Earth and Mars have a little bit of argon in them (1% to 2%). I checked Venus, too, which has 0.007% argon, but that's still more than any other noble gas in the Venusian atmosphere.

I checked the 4 outer gas planets, plus the moon Titan, and for the most part could not find Argon listed in their atmospheric composition. Jupiter is listed as having a very tiny trace amount of Argon that is hard to interpret because it's listing it as relative to helium and then relative to Jupiter/Sun, whatever that means. The moon Titan is listed as having trace argon without specifying any numbers. The others did not mention Argon.

So why do the rocky planets tend to have argon, but the gaseous planets don't?

Why argon specifically? Presumably helium is too light and will float to the top and get knocked away by the solar wind. However, there is one noble gas between helium and argon, namely, neon. So why don't we have neon in our atmosphere instead of argon?

Edit: Maybe the outer planets do have Argon, but it all sank to the bottom and thus we don't detect it? I'm also curious about where Argon lies in the "food chain" of nuclear fusion for an average star like our Sun. I have a hard time seeing how Argon-40 would be more populous than Neon-20 though.


texts: working with stellar spectra in fits format in python

texts:
Hey I am new to working with astronomical data in Python. I wanted to start working with stellar spectra and I am having trouble with the data. To get a first look I just wanted to plot a spectra (flux over wavelength). I downloaded the Miles library (http://research.iac.es/proyecto/miles/pages/stellar-libraries/miles-library.php) and started working with a single fits file. My first steps where as follows :
import numpy as np
import matplotlib.pyplot as plt
from astropy.io import fits

hdul = fits.open('s0013.fits')
data = hdul[0].data
h1 = hdul[0].header

I read the header using print(repr(h1)) and know I wanted to plot the spectrum. The data has shape (1, 4367) and I am not sure how to proceed to achieve 2 arrays one with the wavelength and one with the flux to plot the data. I am sorry if this question is stupid but I can not figure it out.
Cheers


texts: How can I make a good telescope that is powerful enough show nebulae and other deep sky objects ? (consider low budget build)


texts: Is the Local Bubble alone in space or is there another bubble similar to the Local Bubble in space, i.e., do we live in a special place or is this a more general phenomenon?


texts: What possible effects of life replicating on gas giant atmosphere?

texts:
If bacteria managed to arrive then thrive somehow (if not already) on a gas giant could it cause the atmosphere to expand or contract in volume?

Would living matter potentially induce energy into the planets system to heat it up?


texts: What happens over time as a neutron star cools?

texts:
My understanding of a white dwarf star is that, although it hasn't happened yet due to the age of the universe, eventually as it loses energy due to radiating heat and tidal forces, it will cool to become a black dwarf - essentially a black ball of carbon.

What happens when a neutron star eventually cools? What is left, and do we know what it would look like?


texts: Can a galaxy splits into multiple galaxies?

texts: Is there any naturally occurring event powerful enough that can cause a galaxy regardless of shape and size to divide itself into two or more smaller galaxies?


texts:
I'm writing a paper on astronomical seeing. Sir Isaac Newton identified both the phenomenon and origin of astronomical seeing in his Opticks. He writes:

If the Theory of making Telescopes could at
length be fully brought into Practice, yet there would
be certain Bounds beyond which Telescopes could
not perform. For the Air through which we look
upon the Stars, is in a perpetual Tremor; as may be
seen by the tremulous Motion of Shadows cast from
high Towers, and by the twinkling of the fix'd Stars.

is anyone aware of any older reference from Gilbert, Galileo, Harvey, Ptolemy, Copernicus or Kepler?


texts: Differences between alt/az in Stellarium and Astropy

texts:
I've just started to learn Astropy. It's a nifty tool. Using some tutorials, I wrote and then made modifications to a little script that finds the Alt/Az of an object at a certain place and time. I then checked Stellarium's calculation for the Alt/Az of the same object (at exactly the same place and time) and found it to be slightly different. I suspected this was due to slight differences in the underlying coordinates, so I tried manually hard coding the coordinate data for the star from Stellarium; it still came out different. Here is the data without the hard coding:

Object: Rasalhague (alf Oph)
Time: 2018-08-28 23:00 (converted to universal in the script)
Latitude: 35
Longitude: -79
Stellarium reported Az/Alt: +247 35 12.3 / +48 00 57.8
Astropy reported Az/Alt: +247 35 37.4939s / +48 00 08.7586

Manually coding:

RA/Dec on date from Stellarium: 17 35 48.82, +12 32 55.9
Astropy reported Az/Alt: +247 22 42.0379 / +48 09 43.0755

I'm guessing that the difference stems from the conversion algorithm to alt/az.


texts: Why is Saturn invisible in this radar image of its rings?

texts:
The image below is from Radar imaging of Saturn’s rings Nicholson, P. D. et al., Icarus 177 (2005) 32–62, doi:10.1016/j.icarus.2005.03.023 and discussed further in this answer to How did Arecibo detect methane lakes on Titan, and image Saturn's rings?
I believe I can see Saturn's radar "shadow" blocking the furthest parts of the ring near the top of the images, but I can not see any reflections from Saturn itself.
The paper addresses a possible signal from the planet itself in Section 3.2. Ring images:

Echoes at low Doppler shifts might be expected to arise either from near the subradar point on the planet itself or from ring material far outside the main rings. Our images show no evidence for any echo from the subradar point on Saturn, which would appear near ν = 0 and τ = −2RS/c = −402 ms.

The same answer describes radar measurements of Saturn's moon Titan as well.
It might be possible to make a hand-waving argument that Saturn itself is invisible because it's "just gas" but according to ESA's Saturn's atmosphere

The top visible cloud deck, made of ammonia clouds, is found at about 100 kilometres below the top of the troposhere (tropopause), where the temperature is about -250°C.
The second cloud deck, made of ammonium hydrosulphide clouds, is found at about 170 kilometres below the tropopause, where the temperature is -70°C.
The lowest cloud deck, made of water clouds, is found at about 130 kilometres below the tropopause, where the temperature is about 0°C (freezing point of water).

So I'm thinking that the various clouds of different colors and compositions will contain droplets or particles, rather than just be regions of different gas composition.
Why then does there seem to be nowhere near as much radar return from the planet as there is from the rings?


texts: What's the profound reason(s) why the star formation rate drives the scatter of the mass-metallicity relation in galaxies?

texts:
Since decades it's well known that a correlation between stellar mass and metallicity (Z; both stellar and gas-phase Z, but here I focus on the gas-phase Z) exists (e.g., Tremonti+04; analysis of >53000 galaxies from SDSS).
More recent results have shown that the scatter of this "mass-Z" relation is mainly driven by the star formation rate (SFR; e.g., Mannucci+10), i.e., at a fixed stellar mass, galaxies with higher SFRs have lower Z. This happen systematically over a wide range of stellar masses.
What's the physical mechanism(s) responsible for that?

Also, even more recently (e.g., Bothwell+16) it has been shown that the "real" driver of the "mass-Z" relation's scatter is the molecular gas mass (the previously found dependence on SFR may be only a by-product of the Schmidt-Kennicutt relation between gas and SFR).
How this would change the interpretation of the first problem?


texts:
Super-puffs are gas giant sized planets with masses only a few earth masses.
What causes planets to form with such low density and why are they so rare?


texts: Do the cometary gas ions which make up the plasma tail of a comet reach the velocity of the Sun's solar wind?


texts: Is there a possibility that I will find records of stars with masses around 25-30 solar masses within 30 parsecs of solar system. If not, how far do I need to look?


texts: How did the Big Bang occured if before that there was no time?

texts:
I am thinking, that if the Big Bang created time, it implies that before the Big Bang there was no time (correct me if I am wrong).

My question is that, if there was no time before the Big Bang, how did the Big Bang occured ?


texts: What is the reason the Jovian planets are in descending order of size?

texts: Is there any scientific reason for the jovian planets to be in descending order of size or is it purely coincidental? In terms of radii it goes Jupiter, Saturn, Uranus and Neptune.


texts: Why is it hard to reconcile Gaia DR2 with the HIP data set

texts:
I'm trying to get a database of about 20 million of the brightest stars in the sky for a project I'm working on, and I want to reconcile it with the Hipparcos data set.  Currently, I'm only using the HIP dataset for everything, especially the constellations, additionally, as far as I understand, the DR2 data set doesn't have the brightest stars.

My confusion is that for many stars, there is an easy one-to-one correlation, i.e. at 104.304832, 57.563355, I see a magnitude 4.613 star.  This star appears in the HIP dataset as a 6.150 magnitude star.  Roughly the same parallax.  But, if I look at 102.733851, 57.649038, at the 7.44 magnitude star, I see nothing at all in the HIP dataset.

Honestly, most of the stars I'm trying to correlate between the two data sets do not appear.  Is RA/DEC defined differently between the two data sets?  Are they intended to be used as concatenated data sets?  I'd really like to use DR2 to refine the parallax mappings from the HIP data set because for my project estimated distance is so critical.


texts: When are the symbols ⊕ and ♁ used to designate Earth?

texts:
In astronomy I usually see Earth designated with a circled plus or cross. NASA says this is the Earth's astronomical symbol. Wikipedia tends to use it, for example designating the Earth–Moon distance by $\Delta_{\oplus L}$. But Wikipedia also says that the globus cruciger ♁ is used to symbolize Earth.

Does the latter find any usage in astronomy?

(The actual Unicode code point for the circled plus Earth symbol is U+1F728 but this does not render for me, so I used the graphically similar U+2295 instead.)


texts: What's the name for [the other kind of planet] in a binary star system?

texts:
This XKCD what-if talks about rainbows on planets in a binary star system.   It points out that there are two types:

circumbinary planets, where the planet orbits far from and around both stars
[the other kind of planet], where the planet orbits one of the stars and the other star is distant.

What is the proper name for [the other kind of planet] ?


texts: Wher can I find a list of blueshifted regions in the Milky Way?

texts: It would be nice to get a relation between the blueshifted regions and the distance to earth. I'm searching especially for objects in other galactic arms.


texts:
During the polar night directly at the pole the Sun sets once and—after a period of twilight—stays down for months at a time.
The only sources of non-human-made light are the stars, the auroras, and the sunlight reflected by the moon.
Yet when I see various photos of, for example, Amundsen-Scott base during this period, the sky (and the ground illuminated by it) is often quite bright. Here is a timelapse of August, which should be way outside even the civil twilight for this period: https://youtu.be/cf14SL7m8Ys
Is there an issue with photo-sensitivity of the cameras?
Are these sources of illumination actually bright enough to turn the middle of the night into something more twilight-like (if not day-like) when perceived by a human eye? If so, how much of the polar night is actually dark, percentage-wise?


texts: What keeps the planets of the solar system moving in their fixed orbits?

texts:
Models of the solar system show each planet moving around on its own orbit.

Is is really because of the Sun that every planets remains in its own fixed orbit?


texts: The compatibility of the Grand Tack hypothesis with the "core-warping impact" theory of Jupiter's diffuse core

texts:
In recent years, the Juno mission revealed that Jupiter's core was much more diffuse than astronomers had expected.
One theory is that "within a few million years" of its formation, Jupiter experienced a head-on collision with a planetesimal of about $10M_{⊕}$, adding a lot more mass to its core from the silicate planetesimal, but also causing the core's contents to be broken up and mixed with the inner envelope.
The models used in this theory placed Jupiter at a distance of 5.2 AU from the Sun, which is approximately the same as its semi-major axis in the present day. The planetesimal in question would be at the higher end of the valid mass range for a Super-Earth.
Now, according to the Grand Tack theory, Jupiter originally formed at a distance of $\approx 3.5$ AU and migrated inwards toward the Sun, before gravitational interactions with Saturn caused the two planets to move outward and brought Jupiter to its present-day orbit.
Saturn itself would have formed at a distance of $\approx 4.5$ AU, increasing in mass from $30M_{⊕}$ to $60M_{⊕}$ during the first $10^5$ years of Jupiter's inward migration, before starting its own inward migration. This would have been much faster than Jupiter's, enabling Saturn to "catch up" and the gravitational interactions as described to then occur.
The original formations would all have occurred over a timescale of $\lessapprox 6Myr$, maybe closer to $\approx 3Myr$. (The original paper describing the Grand Tack refers only to "a few Myr"; the figures here are based on "Disc Frequencies and Lifetimes in Young Clusters", which it cites in support of this.) The inward and outward migrations would then have occurred in an 800,000 year time period (see Figure 1 of the Grand Tack paper)
(Incidentally, the cores of Uranus and Neptune are each $\approx 5M_{⊕}$ at the start of this migration, increasing to values $> 10M_{⊕}$ at the end of it.)

So far, the two models look quite compatible with each other, with the collision occuring after Jupiter settles into its 5.2 AU orbit. But there is one detail I'm not sure about. Here comes the question:

Descriptions of the Grand Tack theory describe Jupiter as scattering early planetesimals as its gravity disturbed their orbits. Some collided with each other, some were propelled into the Sun... Is it more likely that one of these collided with Jupiter itself at the head-on angle needed for the core-warping collision? Which would mean the impact occurred before Jupiter reached its final orbit.

In addition...

The "few million years" timescale is quite vague. Does anyone know any additional detail which might suggest the impact occurred prior to the Grand Tack's timeframe?

References (not paywalled):
Haisch Jr, K. E., Lada, E. A., & Lada, C. J. (2001). Disk frequencies and lifetimes in young clusters. The Astrophysical Journal Letters, 553(2), L153.
Walsh, K. J., Morbidelli, A., Raymond, S. N., O'Brien, D. P., & Mandell, A. M. (2011). A low mass for Mars from Jupiter’s early gas-driven migration. Nature, 475(7355), 206-209.
Liu, S. F., Hori, Y., Müller, S., Zheng, X., Helled, R., Lin, D., & Isella, A. (2019). The formation of Jupiter's diluted core by a giant impact. Nature, 572(7769), 355-357.
Guillot, T. (2019). Signs that Jupiter was mixed by a giant impact.
with accompanying articles:
Wall, M. (2017). More Jupiter Weirdness: Giant Planet May Have Huge, 'Fuzzy' Core. (space.com)
Weitering, H. (2018). 'Totally Wrong' on Jupiter: What Scientists Gleaned from NASA's Juno Mission. (space.com)
(2019). A core-warping impact in Jupiter's past? (Astronomy Now)
A paper cited in earlier versions of this question but which turned out to be incompatible with the Grand Tack theory:
Pirani, S., Johansen, A., Bitsch, B., Mustill, A. J., & Turrini, D. (2019). Consequences of planetary migration on the minor bodies of the early solar system. Astronomy & Astrophysics, 623, A169.
with accompanying article:
Jupiter's unknown journey revealed


texts: Guess inclination angle from radial velocity measurements

texts:
I came upon this question where the situation is I have radial velocity measurements of a star with two circular orbiting exoplanets and the question is how to find out if the inclination angles of the planets are close to 90°.

From what I understood this question could be resolved using a transit method.

But I don't see how inclination angle can be guessed through radial velocity measurements when they are close to 90°. What difference does it make on radial velocities ?

Update:
I think that the misunderstanding mentioned in the answers was really relevant, indeed in the scope of this problem an inclination of 90° the three points (Star, Exoplanet, observer) are aligned. Which means that a transit can be observed.


texts: How to calculate luminosity in g-band from absolute AB magnitude and luminosity distance?

texts:
How can I calculate the (non-bolometric) luminosity $L$ of a galaxy (or a star for that matter) over a given band from its AB apparent magnitude $m_{AB}$ over that band and its luminosity distance $d_L$?

For instance, consider the g-band which typically has a $\lambda_{eff} = 467 \text{ nm}$ and a $\Delta \lambda = 100 \text{ nm}$. Given this galaxy has an apparent AB magnitude of $m_g = 22.5$ and luminosity distance of $1991 \text{ Mpc}$ (i.e. $z = 0.355$ if you are curious), what is its luminosity? I know I shold use the following equation, but I don't know what value to pick for $M_\odot$.

$$L/L_\odot = 10^{0.4(M_\odot - M)}$$

I tried 5.12 from a website which is the value of $M_\odot$ in g-band but it gives me a different answer compared to when I calculate luminosity using flux:

$$L = 4 \pi d_{L}^2 f_\nu \Delta \nu$$

where $f_\nu$ is flux density and $\Delta \nu$ is the frequency width of the band (this is an approximation to the integration over frequency, assuming bands are step functions). So, how can I find luminosity using absolute magnitude?

Please provide your references.


texts: How was Cassini able to measure and use the Earth-Mars distance to get the Earth-Sun distance?

texts: How was Cassini able to measure and use he distance between Earth and Mars to get the Earth-Sun distance? How were the ratios of Earth-Mars and Earth-Sun calculated then? Given Kepler's laws all we need to now find is orbital period? How did they manage to do this without distance?


texts: Nature and mechanism of the short-term variability in radio strength of Sgr A*?

texts:
The Phys.org article Cosmic filament probes our galaxy's giant black hole links to A Nonthermal Radio Filament Connected to the Galactic Black Hole? which discusses (among other things) the importance of achieving high dynamic range to study these filaments in the proximity of the strong emission associated with Sgr A*. It mentions the fluctuation of radio intensity from Sgr A* on time scales as short as five minutes (as well as to instrumental time-varying effects that also require attention and calibration).

The paper refers to Zhao et al. 2016, which in turn links to Zhao et al. 1999. But so far I can't track down either the nature of the short term variations seen in the radio brightness of Sgr A* nor the mechanism.

What is the nature of this variation (amplitude, power spectrum, any periodicity?) and what are the proposed mechanisms?


texts: I'm reworking my question regarding magnification of my 60mm, ⨍=700mm refractor. The video eyepiece is a CMOS sensor with a pixel size of 5.6μ x 5.6μ. The number of pixels is 720 X 480 with a 0.3 megapixel resolution. That said, I'm clueless regarding an algorithm from which you could decipher the magnification given these physical characteristics of the CMOS sensor. Any thoughts would be appreciated. Thank you!


texts: The role of gravity during planetesimal accretion

texts: As far as I understand, during the formation of a planetary disc, grains of dust stick together due to collisions and chemical bonding. Considering the size of the grain - say, 1 mm - and the speed - 1cm per sec - it would seem that gravity plays a minor role during accretion. My question is, to what extent is gravity a factor during accretion? To what extent is it related to fragmentation? In other words - how does gravity affect whether the fragments return and stick to the main body? Is there a size barrier, or is it dependent only on the speed?


texts: What is it exactly about these flares of infrared light from Sgr A* that "confirms" it is a supermassive black hole?

texts:
CNET.com's SCI-TECH
Scientists confirm a 'supermassive black hole' at the heart of our galaxy
It's "mind-boggling", they say.

This links to Astronomy.com's Scientists finally confirm the Milky Way has a supermassive black hole
This links to ESO's eso1835 — Science Release Most Detailed Observations of Material Orbiting close to a Black Hole; ESO’s GRAVITY instrument confirms black hole status of the Milky Way centre

FYI, the GRAVITY instrument measures infrared light, not gravity.

What is it exactly about these flares of infrared light from Sgr A* that confirms it is a supermassive black hole?

Certainly there is plenty of evidence, the orbits of stars nearby for one. But this use of the word confirm seems strong and frequent enough to suggest the deal has been done, the ink is dry, and it's a black hole without question and that until now that wasn't so.

I've shamelessly absconded the following images from this answer to the question What is the evidence for a supermassive black hole at the center of Milky Way?, which may need a new answer!

Note, the size of these stellar orbits are compared to those of Sedna, Eris, Pluto and Neptune in the bottom right corner (same scale)!

Source


texts: What are the Kinematics / Dynamics behind the motion?

texts:
https://www.timeanddate.com/eclipse/in/@8133395?iso=20200621
The link I have attached is a predicted model for the eclipse in my area! I am very much confused about the movement of the moon analogous to the video in the link. Community, The movement seems like a parabola curve and no-doubt the model is telling it very well. In other ways, the motion also appears as bouncing of an object! I might have interpreted it in wrong sense or maybe not but that's no matter of concern ;-). A detailed answer would be a piece to take away from this question. Also, I suppose it to be a matter of Orbital Dynamics.
-


texts: How does the size of a naked black hole effect its photon sphere?

texts:
What effect does the size of a black hole have on the size or density of the photon sphere and it's proximity to the horizon?

For example: A person is in space looking at 2 black holes, one of them big and the other small. Could the bigger one appear smaller because of the way space bends around it?

If yes, can a large enough black hole be completely hidden behind the gravitational lensing? Could a dense photon sphere around a black hole look like a spherical distortion to distort the horizon or hide the black hole completely?


texts: How do astronomers convert radio signals received by their antenna to images?

texts:
I'm very new to radio astronomy and I am curious how an the signals received by a radio antenna are converted to data on a computer and then images? Is there a popular software to use for this, or do astronomers typically write their own code?
Thanks in advance!


texts: How can you estimate distance of an object by its redshift?

texts: Is there a way to take the red shift of an object and, from that, calculate a rough estimate of its distance from us (in parsecs, preferably)?


texts: Are nebulae only visible from a distance?

texts:
There's plenty of data about the density of nebulae, and obviously they're pretty thin.  This is space, after all, and these things are really, really big.

But I'm wondering about the practical experience of that density.  Are the colorful patterns of gas only visible when you're far away and looking through them, or if you were inside a nebula would you see colors all around you instead of the black of space?  Are any dense enough to obscure the view between planets of the same solar system?  Between a planet and its moon?


texts: Why does the cloud of Orion Nebula appear more distinct when I am not directly looking at it?

texts: I have a 6cm aperture newtonian refractor telescope through which I saw the Orion Nebula yesterday night. As all you can hope with a telescope of such a small aperture, I saw some faint cloudy structure, but when I looked away from the cloud through the telescope it appeared to be more distinct and dense. Why is it so?


texts: Calculation of right ascension and declination

texts:
I am confused about this problem:

If I see an object from Mount Teide (longitude is 16"30'E and latitude is 28"18'N) that passes the meridian (azimuth=0) at 5h (am) UTC, and I also know that the elevation of the star is 43"40', the stellar time at Greenwich at 0h UTC is 22h20min.

How can I calculate the right ascension and declination?


texts: How fast was the Earth spinning directly after the Moon formed?

texts: I understand the Moon was perhaps five Earth radii away when it first formed (assuming it was formed by a giant impact of a Mars-sized body), and Earth has since transferred its rotational energy into the moon's orbital energy. How fast would Earth have been spinning at the point the Moon was formed? Assuming it was spinning very fast (day under 10 hours) would this have caused a noticeable decrease in effective "gravity" at the equator? Presumably the Precambrian microbes could have reached equatorial orbit really easily, assuming they had a space program.


texts:
This questions concerns the longitudinal aspect of the Equation of Time, also called the Equation of the Center. In some sources the equation looks like the following:

$\nu - M = 2\varepsilon \sin M$       (1)

where $\nu$ is the True Anomaly of the Sun's position from the Earth, $M$ is the Mean Anomaly, and $\varepsilon$ is the eccentricity of the Earth's orbit (0.0167). $\nu - M$ is the difference between the Sun's actual angle and the and the angle that would exist if the Earth's orbit were circular.

Other sources have a first-order approximation that looks like the following:

Time deviation (minutes) = $-7.655 \sin d$       (2)

where d is the day of the year.

My difficulty is reconciling these two equations. None of the sources actually make this connection explicit. I assume that the difference has to do with converting angles and times, and I have tried various approaches to making the numbers work out, without avail. I would appreciate it if someone could tell me how the value of -7.655 minutes is derivable from $2 \varepsilon$ and or point me at a resource that demonstrates the connection between them.

(Note I realize that both (1) and (2) are approximations. At this stage, I am trying to understand the situation in its simplest form before adding refinements.